Fifteen years after he first donned that freshly pressed doctor's coat, Noah Wyle is revealing an "ER" secret: There are only about 12 things you can do to a patient in the emergency room before shipping them elsewhere in a hospital.

"You've got your intubation, your thoracotomy, your chest tube, your central line . . . once you have those memorized, you can do anything," he said.

Well, more or less. In the series' pilot episode, Wyle's first-year emergency room intern John Carter, vocabulary down pat, thinks he's ready to do some good at Chicago's County General. Behind his back, the exhausted residents mock his spanking-white jacket and clipboard at the ready. He has no idea what's about to hit him.

Neither did the 23 million viewers who showed up to watch that first 24-hour shift, shot in East L.A.'s historic Linda Vista Hospital: a daunting, painstakingly well-choreographed maze of rapid-fire medical jargon, wheeling gurneys, no-nonsense nurses, huffy surgeons, neglected spouses, a sexy pediatrician, a taxicab-delivered woman in labor and no coffee.

"I remember even then we were all using George Clooney as a barometer of our success," Wyle said. "He was the only one with enough TV experience to explain that a '40 share' meant we were a hit."

During his first day, Carter sutures minor injuries, takes some verbal abuse from his senior resident and, on his first solo run with a patient, sticks the loud, cranky Frank (who later returned to the series as the department's desk clerk, played by Troy Evans) several times to rig him to an IV. "I wanted to make Carter clumsy, naive, give him these physical tics," Wyle said. The task, he admitted, was made easier by the actor's shaky audition in which he performed the same scene.

"[Late series creator] Michael Crichton gets all the credit," he said. "I couldn't get out of my own head, and so Michael told me this anecdote that was totally unrelated to anything about the show. It loosened me up and I walked out with a job."

A job as a waiter at the Bel Age Hotel's Diaghilev restaurant also helped ease nerves. "I swear, it was the perfect training," he said. "We did what the maitre d' liked to call these 'silent ballets': moving around customers and presenting the food. Honestly, it's the same stuff we did on 'ER': weaving around gurneys and under booms and Steadicams."

Wyle, just 23 when he began playing Carter, said he remembers feeling like he had found something special. "I was under the misunderstanding that it was a feature script that I was reading," he recalled. "Then I found out it was for TV and thought, 'Oh, well, it'll be well-received, scantily watched and canceled in six episodes.' I'd take the money and go back to film and theater."

Instead, he and subsequent casts would try to recapture that first episode's style and rhythm, "that magic, really," he said, every week for the next 15 years. "It was so innovative for its time -- the pace, the long, uninterrupted takes in and out of rooms. It's standard operating procedure on television now, but we knew even then that we were a part of something really great."